Re: [RFC][PATCH 0/2] CR: save/restore a single, simple task

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting Oren Laadan (orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org):
> 
> In the recent mini-summit at OLS 2008 and the following days it was
> agreed to tackle the checkpoint/restart (CR) by beginning with a very
> simple case: save and restore a single task, with simple memory
> layout, disregarding other task state such as files, signals etc.
> 
> Following these discussions I coded a prototype that can do exactly
> that, as a starter. This code adds two system calls - sys_checkpoint
> and sys_restart - that a task can call to save and restore its state
> respectively. It also demonstrates how the checkpoint image file can
> be formatted, as well as show its nested nature (e.g. cr_write_mm()
> -> cr_write_vma() nesting).
> 
> The state that is saved/restored is the following:
> * some of the task_struct
> * some of the thread_struct and thread_info
> * the cpu state (including FPU)
> * the memory address space
> 
> [The patch is against commit fb2e405fc1fc8b20d9c78eaa1c7fd5a297efde43
> of Linus's tree (uhhh.. don't ask why), but against tonight's head too].
> 
> In the current code, sys_checkpoint will checkpoint the current task,
> although the logic exists to checkpoint other tasks (not in the
> checkpointee's execution context). A simple loop will extend this to
> handle multiple processes. sys_restart restarts the current tasks, and
> with multiple tasks each task will call the syscall independently.
> (Actually, to checkpoint outside the context of a task, it is also
> necessary to also handle restart-block logic when saving/restoring the
> thread data).
> 
> It takes longer to describe what isn't implemented or supported by
> this prototype ... basically everything that isn't as simple as the
> above.
> 
> As for containers - since we still don't have a representation for a
> container, this patch has no notion of a container. The tests for
> consistent namespaces (and isolation) are also omitted.
> 
> Below are two example programs: one uses checkpoint (called ckpt) and
> one uses restart (called rstr). Execute like this (as a superuser):
> 
> orenl:~/test$ ./ckpt > out.1
> hello, world!  (ret=1)		<-- sys_checkpoint returns positive id
>  				<-- ctrl-c
> orenl:~/test$ ./ckpt > out.2
> hello, world!  (ret=2)
>  				<-- ctrl-c
> orenl:~/test$ ./rstr < out.1
> hello, world!  (ret=0)		<-- sys_restart return 0
> 
> (if you check the output of ps, you'll see that "rstr" changed its
> name to "ckpt", as expected).
> 
> Hoping this will accelerate the discussion. Comments are welcome.
> Let the fun begin :)

Compile, boot, and c/r-tested on my f9 kvm image.

-serge